The Denoiser will first try to use CUDA, if it doesn't find a compatible card, it will fallback to OpenCL GPU (usually with AMD and Intel cards)and then . If the image doesn't fit in the graphics card memory, you can then use OpenCL with CPU (which will use RAM memory).

Note

Maxwell 4 is compiled for 64-bit ONLY. It requires a 64-bit machine and a 64-bit operating system. Plugins are available only for 64-bit builds of their respective host platforms.